short and chubby tardigrades They are among the smallest legged animals on Earth, and these microscopic waters carry wood like chubby little babies. But most creatures as small as tardigrades don’t even have legs, so scientists recently analyzed tardigrades’ locomotion to better understand how they use their limbs.
Tardigrades, also known as moss pigs, have segmented bodies and four pairs of legs. They scurry across deep-sea sediments and sandy river bottoms, rushing over them lichens And moss on the ground, trotting toward potential mates and food or away from predators.
Snapshots of bad tardigrades in species Hypsibius style She revealed that their movements are very similar to those in insects about 500,000 times their size, although they are separated by about 20 million years of evolution and belonging to a different phylum. The new study finds that the step patterns of insects and other arthropods (invertebrates with segmented bodies and articulated legs) change when animals speed, and tardigrades’ steps follow similar patterns when they walk faster.
Related: 8 reasons why we love tardigrades
Tardigrades, of which there are about 1,300 known species, are notorious for being tough to kill. They can survive exposure to extreme temperatures, solar radiation And emptiness of space. Few studies have examined these tough creatures in more typical conditions, said lead author Yasmin Nerudi, an independent researcher and fellow in the Rockefeller Center for Studies at Rockefeller University, and before the new study, scientists knew nothing of how tardigrades walk. Physics and Biology in New York City.
Most microscopic animals with soft bodies do not have legs, so it is also difficult to notice exactly how these small animals move. By analyzing tardigrades, literally one step at a time, the researchers also hoped to uncover clues about movement in general on a very small scale, Nerudi told Live Science.
“We’ve seen tardigrades give us this niche in these two things that we don’t know much about,” Nerudi said.
Nerudi’s team looked at adults in these species H style.They are up to 0.02 inches (0.5 mm) long. All eight of their legs are structurally similar, but the pair closest to their hind ends have less muscle than the others. Scientists reported August 31 in the journal that while this pair of legs plays some role in locomotion, most of the hard work is split between the other six limbs. Proceedings of the National Academy of Sciences (PNAS).
At first, the researchers tested tardigrades on smooth glass slides, but they found that the water bears had difficulty pushing themselves over the slippery surface. It was easier for tardigrades to walk when they could dig and dart with their claws. For the rest of the experiments, tardigrades were moving over a gel that compressed their paw, according to the study.
Unlike larger animals that can be induced to walk or run, Nyrodi said, tardigrades are too small for researchers to stimulate their movement. So the scientists set up microscopes and cameras in the lab, left the tardigrades loose…and then waited.
“You get hours and hours of shots,” Nerudi said. “And I watched it all.”
The name of the phylum Tardigrada (tardigrades being the only member) comes from the Latin word “tardigradus” or “slowly,” and the tardigrades in the study lived up to that name. When they were moving at a comfortable pace, they traveled about half their body length per second—about 0.01 inch (0.25 mm)—and at a higher speed, they covered about two body lengths per second.
And when tardigrades shifted gears between slow and fast walking, they smoothly transitioned to a new stride pattern, as many arthropods do, rather than switching to a new gait—the body’s center of gravity also shifts—as is common in animals with a backbone.
When arthropods (and tardigrades) walk slowly, they lift one foot at a time. When they speed up, they lift two feet diagonally apart across the body. Faster speeds cause the animals to move into a new pattern in which they are three feet off the ground at a time: a front foot and a back foot on one side of the body, and a middle foot on the other.
“These patterns are tightly regulated by speed, they travel well between five legs on the ground, four legs on the ground, and then three legs on the ground as their speed increases,” Nerudi said. In experiments, tardigrades showed that they followed the same pattern in which the legs were carried in the air when the other legs were on the ground.
But why do tardigrades walk like arthropods? Groups can have a common ancestor that has been linked to bots in this way. However, it is also possible that arthropods and tardigrades may have evolved this gradient pattern independently, after their lineages diverged, according to the study.
“What that means is that while there are very different body structures, body sizes and the environments they move through, there is just something about this specific coordination scheme that is effective in all of these conditions,” Nerudi said.
Originally published on Live Science.